An atom is the smallest particle that can be described as a chemical.
- At the centre of an atom is a nucleus containing protons which are positively charged sub-atomic particles. The number of protons determines the chemical element associated with the atom. A hydrogen atom has a single proton.
- The nucleus of an atom also contains neutrons, sub-atomic particles with a mass slightly greater than that of a proton but no positive or negative charge.
- Surrounding the nucleus are negatively charged particles called electrons which are held in place by their attraction to the positively charged protons in the nucleus.
- In an atom, the number of electrons matches the number of protons.
- When an electron is added or removed from an atom it forms a charged particle called an ion.
- A cation is a positively charged ion with fewer electrons than protons.
- An anion is a negatively charged ion with more electrons than protons.
- The number of protons and neutrons combined determines the atomic mass of an atom.
- Atomic mass is a measure of the total mass of protons and neutrons in an atom and is illustrated by the ordering of elements in the periodic table.
- In atomic theory and quantum mechanics, an atomic orbital is a mathematical function describing the location and motion of electrons around the nucleus of atoms.
Related diagrams
The diagram below can be viewed on its own page with a full explanation.
